Resolutions that aren't divisible by 4 lead to VC:MP's screenshots being torn and distorted because it doesn't scale to a resolution that is divisible by 4. 1366 isn't evenly divisible by 4, so the screenshots you take in VC:MP are broken. If I recall correctly, this is an issue with screen capturing in DirectX.
FRAPS takes 1366x768 screenshots and scales them to 1360x768, which is divisible by 4, so screenshots are taken properly by it.